Lubricating oil base stock production by hydrocracking two separat feed-stocks

ABSTRACT

A MULTIPLE-STAGE PROCESS FOR PORDUCING LUBRICATING OIL BASE STOCKS HAVING VISCOSITY INDICES GREATER THAN ABOUT 100. THE HEAVIER PORTION OF THE CARGE STOCK, HAVING AN INITIAL BOILING POINT IN THE RANGE OF ABOUT 800*F.TO ABOUT 925*F., IS SEPARATELY PROCESS IN A FIRST STAGE. THE FROT END OF THE RESULTING PRODUCT EFFUENT IS PROCESED IN A SECOND STAGE, IN ADMIXTURE WITH THE LIGHTER PORTION OF THE CHARGE STOCK HAVING AN END BOILING POINT IN THE RANGE OF ABOUT 800*F. TO ABOUT 925*F. A SERIES OF SEPARATION STEPS IS EMPLOYED TO RECOVER THE LUBRICATING OIL BASE STOCK WHILE CONCENTRATING A HIGH VISCOSITY INDEX BRIGHT STOCK

United States Patent O U.S. Cl. 208-59 10 Claims ABSTRACT OF THE DISCLOSURE A multiple-stage process for producing lubricating oil base stocks having viscosity indices greater than about 100. The heavier portion of the charge stock, having an initial boiling point in the range of about 800 F. to about 925 F., is separately processed in a rst stage. The front end of the resulting product eluent is processed in a second stage, in admixture with the lighter portion of the charge stock having an end boiling point in the range of about 800 F. to about 925 F. A series of separation steps is employed to recover the lubricating oil base stock while concentrating a high viscosity index bright stock.

APPLICABILITY OF INVENTION The present invention involves the catalytic conversion of hydrocarbons in a multiple-stage process. More particularly, the present invention is directed toward the production of lubricating oil base stocks having viscosity indices above 100. A lubricating oil base stock is synonymously referred to in the art as neutral oil, and is, in effect, a dewaxed hydrocarbon mixture boiling in the lube oil boiling range -which does not contain viscosity improvers or other additives. That is, a lubricating oil denotes in the art a dewaxed product containing various additives. Through the utilization of the present invention there is produced a waxy lubricating oil base stock having a viscosity index substantially above S100. Following dewaxing, a standard prior art technique, the viscosity index remains above 100, and the resulting neutral oil is highly desirable for the production of multi-graded lube oils.

The prior art is replete with references to crude oils containing hydrocarbon components which are suitably adaptable for use as lubricating oils. In general, those lubricating oils derived from highly parailinic crude stocks are utilized in the production of high quality motor oils, aviation oils and turbine oils. Such a lubricating oil is characterized by a relatively high viscosity index (V.I.), although, it is actually a blend of relatively low and relatively high viscosity index components. Lubricating oil base stocks which are derived from highly naphthenic crudes are employed in the production of lubricating oils having exceptionally desired properties with respect to heavy duty use such as that found in diesel engines. Desirable components of lubricating oil base stocks, or neu tral oils, are isoparaflins and molecules containing single rings, whether naphthenic or aromatic. However, essentially all heavy hydrocarbonaceous fractions, derived from crude oils, contain condensed-ring aswell as straight-chain hydrocarbons. The condensed-ring hydrocarbons characteristically have low viscosity indices and relati-vely poor resistance to oxidation. Therefore, they are undesirable as components of the various types of lubricating oils.

A perusal of the prior art procedures and techniques for producing lubricating oil base stocks, indicates that relatively high viscosity index lubricating oils may be produced through the use of a combination of solvent extraction and clay-treating, acid-treating, etc. Heavy 3,649,518 Patented Mar. 14, 1972 duty lubricating oils are generally obtained by way of vacuum distillation followed by alkali-treating for the removal of naphthenic acids. The complex nature of high viscosity index lubricating oil production presents a challenge to the petroleum industry in addition to giving rise to signicant processing problems which are not easily solved through the use of present-day operating techniques. For example, solvent extraction of the undesirable components is ineicient in view of the fact that the available solvents are not highly selective for the cornponents which must be removed from the lubricating oil base stock. Furthermore, immense, complicated equipment is required for contacting the lubricating oil with the solvent and for the recovery of the various solvents in order to make the process economically attractive. With respect to acid-treating and clay-treating techniques, problems involve the disposal of clay, and loss of hydrocarbon yield, as well as an acidic sludge disposal problem when strong acids, such as sulfuric acid, are employed. By way of brief summary, it might be said that the prior art schemes are severely limited in their capability to produce pure lubricating oils having high viscosity indices, and are tedious and expensive to operate in an acceptably ecient manner.

Candor compels recognition of the fact that certain prior art techniques are necessary if satisfactory lubricating oils are to be produced. Thus, it is necessary to subject the crude oil to one or more distillation techniques in order to provide a crude oil bottoms concentrated in lubricating oil base stock. Another prior art scheme, which may be required as a preliminary processing step with respect to some crude oil bottoms, is a deasphalting process. The crude oil bottoms, containing asphaltenic constituents, is intimately admixed with a light hydrocarbon solvent such as propane, pentane or heptane at conditions of temperature and pressure under which the alphaltenic constituents are precipitated. Since the preliminary processing techniques of distillation and deasphalting are Well known to those skilled in the art of petroleum relining techniques, and further form no essential part of my invention, additional description thereof is not believed required herein.

Another prior art technique is necessary to produce a suitable lubricating oil base stock. Waxy constituents must be removed in order to improve the quality of the ultimate lubricating oil. The dewaxing technique is accomplished by well :known methods which generally employ solvent such as propane, methylethyl ketone, toluene, etc. The waxy lubricating oil base stock and solvent are generally heated to a temperature sufliciently high to render the solvent and oil substantially miscible. The resulting mixture is then chilled to precipitate the Wax from the solution. As hereinafter indicated, the dewaxing step adversely affects the viscosity index.

OBJECT S AND EMBODIMENTS A principal object of the present invention resides in the production of a maximum yield of lubricating oil base stocks. A corollary objective is to produce a dewaxed lube oil base stock pool having a flat viscosity index profile, wherein viscosity index prole is defined as the change in VI. as a function of viscosity of the lube oil cut taken from the lube oil base stock pool.

Another object of my invention is to produce lubricating oil base stocks having viscosity indices greater than from different fractions of a crude oil.

Before describing the various embodiments of the present invention, a brief reference to the accompanying drawing, in conjunction with the terms employed in the embodiments and appended claims, may be helpful in 3 obtaining a clear understanding of the invention. Therefore, referring briefly to the drawing:

(1) First hydrocarbon charge stock 1s the deresined oil being introduced by way of line 1.

(2) First hydrocracking reaction zone is reactor 6,; (3) Second, lower-boiling hydrocarbon charge stoc is the waxy distillate entering the process by way of line 14. a,

(4) Second hydrocracking reaction zone is reactor 13.

(5) First separation zone is'hot separator 8, and produces a first vaporous phase 1n line 12 and a first liquid phase in line 9.

(6) Second separation zone is hot separator 18, and pro-vides a second vaporous phase in line 19 and a second liquid phase in line 23.

(7) Third separation zone is cold separator 20 and provides a third vaporous phase in line 2 and a third liquid phase in line 21.

(i8) The fourth separation zone is hot flash chamber 10, and provides a fourth vaporous phase in 11 and a fourth liquid phase in line 27.

(9) Fifth separation zone is hot iiash chamber 24, and provides a iifth vaporous phase in line 25 and a fifth liquid phase in line 26.

(10) Sixth separation zone is cold flash chamber 22, and provides a sixth liquid phase in line 32 and a sixth vapor phase in line 38.

(11) Seventh separation zoue is vacuum column 28 and provides a seventh liquid phase in line 31, an `eighth liquid phase in line 29 and a ninth liquid phase in line 30. Not illustrated is the normally vaporous phase which is removed by way of the vacuum jets.

(12) Eighth separation zone is fractionator 33, providing a tenth liquid phase as a bottom stream in line 37.

In achieving the foregoing objects, my invention provides a process for producing a lubricating oil base stock which comprises the steps of: (a) reacting a first hydrocarbon charge stock and hydrogen in a first hydrocracking reaction zone, at hydrocracking conditions, in contact with a hydrocracking catalyst; (b) separating the resulting rst zone effluent at substantially the same temperature and pressure in a first separation zone, to provide a rst principally vaporous phase and a first principally liquid phase; (c) reacting said first vapor phase and a second, lower-boiling hydrocarbon charge stock in a second hydrocracking reaction zone, at lower severity hydrocracking conditions, and in contact with a hydrocracking catalyst; (d) separating the resulting second zone eiiuent at substantially the same pressure and temperature in a second separation zone, to provide a second principally vaporous phase and a second principally liquid phase; (e) separating said second vaporous phase, at substantially the same pressure and at a lower temperature in the range of about 60 F. to about 140 F., in a third separation zone, to provide a hydrogen-rich third vaporous phase and a third principally liquid phase; (f) recycling at least a portion of said hydrogen-rich third vaporous phase to combine with said tirst hydrocarbon charge stock; and, (g) separating said first, second and third liquid phases to recover said lubricating oil base stock.

Other objects and embodiments of my invention involve particularly preferred operating conditions and techniques, as well as the catalytic composites utilized in the hydrocracking reaction zones. One such embodiment relates to the lower-severity conditions employed in the second hydrocracking reaction zone. Particularly included are a lower maximum catalyst bed temperature, a higher liquid hourly space velocity, or both. One other such embodiment involves a first hydrocarbon charge stock having an initial boiling point in the range of about 800 F. to about 925 F. while the second hydrocarbon charge stock has an initial boiling point above about 600 F. These, as well as other objects and embodiments of my invention, will become evident from the following more detailed summary of the present lubricating oil base stock producing process.

SUMMARY OF INVENTION The hydrocarbon charge stocks, applicable for use in the present process, are conventional and well known in petroleum refinery technology. Thus, suitable charge stocks include vacuum gas oils, propane deasphalted oils, reduced crude stocks, mixtures thereof, etc. One illustrative feed stock is a mixture of 44.5 vol. percent of a raw waxy neutral oil, 23.6 vol. percent heavy vacuum gas oil, and 31.9 vol. percent deasphalted oil. This charge stock indicates a gravity of about 24.4 API, an initial boiling point of 640 F., a 50.0% volumetric distillation temperature of about 899 F., and an end boiling point of l106 F. This feed stock is contaminated with undesirable materials as indicated by the presence of about 0.42% by weight of sulfur and 1,300 p.p.m. by weight of nitrogen. Another such charge stock is a top vacuum gas oil derived from an Illinois crude having a gravity 0f 22.3 API, an initial temperature of 905 F. and an end boiling point of about 1050" F. The vacuum gas oil contains 1,630 p.p.m. by weight of nitrogen and 0.44% by Weight of sulfur.

The multiple-stage process of the present invention is a catalytic process with the catalytic composites being disposed as iixed-beds in the respective reaction zones. Although the precise composition of the catalyst need not necessarily be identical in all stages, the catalytically active components are generally selected from the metals of Groups VI-B and VIII of the Periodic Table, and are composited with a porous carrier material. In many applications, the catalytic composite may also contain a halogen component, generally from the group of chlorine, fluorine and mixtures thereof. The porous carrier material is necessarily refractory with respect to the operating conditions employed in the hydrocracking reaction zones, and it is intended to include those carrier materials which have traditionally been utilized in effecting the hydrocracking of hydrocarbonaceous material. In particular, suitable carrier materials are selected from the group of amorphous refractory inorganic oxides including alumina, silica, titania, zirconia, magnesia, boria, alumina-silica, silicamagnesia, alumina-silica-boron phosphate, slica-zirconia, etc. When of the amorphous type, one preferred carrier material constitutes a composite of alumina and silica, with silica being present in an amount of about 10.0% to about 90.0% by weight. In many applications of the present invention, the carrier material may consist of a crystalline aluminosilicate. This may be naturally-occurring or synthetically-prepared, and includes mordenite, faujasite, Type A or Type U molecular sieves, etc. When utilized as the carrier, the zeolitic material may be in the hydrogen form or in a form which results from treatment with multi-valent cations. No particular refractory inorganic oxide carrier material is essential to the present invention, and it is intended to include within the scope of the present invention all conventional carrier materials, as well as the wide variety of methods for the preparation thereof.

Preferred catalytic composites contain at least one metallic component from Ithe metals of Groups VI-B and VIII as set forth in the Periodic Table of the Elements, E. H. Sargent and Company, 1964, although it is understood that equivalent results are not achieved through the indiscriminate selection of metallic components. That is to say, a mixture of chromium and cobalt components will not yield results equivalent to those obtained through the use of molybdenum and nickel components. Suitable metallic components include chromium, molybdenum, tungsten, iron, nickel and cobalt, as well as the noble metals of Group VIII, ruthenium, rhodium, palladium, osmium, iridium and platinum. The Group VIII noble metal components generally comprise about 0.01% to about 2.0% by weight of the final composite, calculated on an elemental basis. The noble metal components may be incorporated within the catalytic composites in any suitable manner including co-precipitation or cogellation, ion-exchange or impregnation. When utilized as a component of the catalytic composite, the metals of Group VI-B, chromium, molybdenum and tungsten are utilized in an amount of from about 4.0% to about 30.0% by weight. The iron-group metal components, iron, cobalt, and nickel, will be employed in an amount Within the range of about 1.0% to about 10.0% by weight. These metallic components may also be composited with the porous carrier material in any suitable manner well known and thoroughly described within the prior art.

The hydrocracking process of the present invention eliminates the necessity for an initial extraction operation; however, as hereinbefore set forth, a final dewaxing technique is necessarily practiced. Whereas solvent extraction removes those components having a low viscosity index without chemical reaction being effected, hydrocracking simultaneously converts the components of low viscosity index into high quality naphthas and distillates, and the components of high viscosity index to a lesser extent, whereby the same continue to be within the desired boiling range of lubricating oils. During the hydrocracking of heavy distillates for the production of lubricating oil base stocks, the viscosity index profile, defined herein as being the viscosity indices of 10.0% by volume fractions of the total waxy lubricating oil, plotted as a function of volume percent distilled, indicates low viscosity indices on the front end, and higher viscosity indices on the heavier ends. Thus, the viscosity index profile of the total waxy lubricating oil base stock pool typically indicates from about 10.0% to about 30.0% by volume having a viscosity index below about 100, with the incremental viscosity indices increasing to values above 100, and often into the 130 to 140 range. It is very desirable to have the viscosity indices of all the dewaxed 10.0 vol. percent fractions above 100. A preferred waxy lubricating oil base stock pool is one where the initial 3 to 4 dewaxed 10.0% fractions each have a viscosity index of about 103 to 106. Were an attempt made to process the entire portion of a reduced crude suitable for hydrocracking for lube oil production at an operating severity such that the waxy viscosity index of the front end is at least about 105, the overall yield of lubricating oil base stock potential is decreased about 5.0% to about 15.0% by volume, based upon fresh feed, and the viscosity index of the lighter oils is much higher than required.

In accordance with the present invention, the original reduced crude is separated to provide a heavy vacuum distillate (waxy distillate fraction) and a heavy residual cylinder stock, from -which is derived the deresined oil hereinafter referred to. The initial boiling point of the cylinder stock, or the deresined oil is in the range of about 800 F. to about 925 F., depending upon the character and quantity of the resins, as well as that of the low -viscosity index condensed-ring compounds. Another consideration is the quantity of asphaltenic compounds contained in the fresh feed charge stock. The operating conditions necessarily imposed, with respect to a single-stage unit, in order to improve the viscosity index of the neutral oil fraction of the deresined oil, are such that excessive cracking of the higher-boiling fractions is experienced. Although such a unit will produce a lubricating oil base stock pool having a viscosity index prole above about 100, the volumetric yield thereof, based upon the fresh feed charge stock, is significantly decreased. The present scheme oiiers a modified series iiow wherein the heavy cylinder stock fraction is processed separately from the lighter, waxy distillate fraction. In the absence of the lighter material, the tirst stage can function acceptably at a higher operating severity -with the result that a lesser quantity of lubricating oil components are converted into lower boiling products such as naphtha and kerosene fractions, and the desired high viscosity base stocks of V.I.s above are produced from the heavier material. The product efiiuent, from the reaction zone in which the deresined oil is processed, is separated in a hot Separator at substantially the same pressure and temperature to provide a principally vaporous phase containing same hydrocarbons boiling up to a temperature of about 1000 F. This front end fraction is then combined with the lighter waxy distillate for processing in the second stage of the process. In the absence of the heavier material, the second stage can function acceptably at the necessary operating severity with the result that the desired V.I. is achieved. Individual separation trains are utilized to concentrate and recover a high viscosity index bright stock separate from the waxy lubricating oil base stock product of the process. This permits back-blending of the bright stock with various neutrals derived from the lubricating oil base stock for the production of intermediate viscosity lube base stocks. Where desired, the Waxy bright stocks may be recycled to combine with the deresined oil, without or `with a diluent stream, in order to achieve additional cracking thereof into the lower-boiling lubricating oil components.

The hydrocarbon charge stock and hydrogen are contacted with a catalyst of the type hereinabove described in a hydrocracking reaction zone. The particular catalyst is primarily dependent upon the characteristics of the charge stock, as well as the desired end result. Although the catalytic composite may be the same in both hydrocracking reaction zones, many situations arise wherein enhanced results are achieved through the use of different catalytic composites. The contacting may be accomplished by using the catalyst in a fixed-bed system, a moving-bed system, a moving-bed system, a fluidized-bed system, or in a batch-type operation. However, in view of the risk of attrition loss of the catalyst, it is preferred to use a fixed-bed system. Furthermore, it is Well known that a fixed-bed catalytic system offers many operational advantages. The reactants may be contacted with the catalyst in either upward, `downward or radial oW fashion, with a downward flow being preferred. Additionally, the reactants may be in the liquid phase, a mixed liquidvapor phase, or a vapor phase when they contact the catalyst.

The specific operating conditions imposed -upon the individual hydrocracking reaction zones are primarily dependent upon the physical and chemical characteristics of the fresh feed charge stock. However, with respect to the first hydrocracking reaction zone, wherein the heavy yderesined oil is processed, the operating conditions will include a pressure from about 1,500 to about 3,000 pounds per square inch, and LHSV (liquid hourly space velocity) of about 0.3 to about 3.0, and a hydrogen concentration in the range of about 3.000 to about 15,000 scf/bbl. In view of the fact that the hydrocracking process is exothermic in nature, an increasing temperature gradient will be experienced as the hydrogen and feed stock traverse the catalyst bed. It is preferred that the maximum catalyst bed temperature, in the lirst hydrocracking reaction zone, be maintained in the range of about 700 F. to about 900 F.

As hereinbefore stated, the product eiiiuent from the first hydrocracking reaction zone is separated to provide a front end which is combined with the waxy distillate, the mixture being the charge to the second hydrocracking reaction Zone. The second hydrocracking reaction zone can then be maintained at a lower severity of operation than would be required if the waxy distillate were processed with the heavier fraction. This lower severity operation is achieved either by decreasing the maximum catalyst bed temperature, increasing the liquid hourly space velocity, or through a combination of these changes in both operating variables. Thus, although the hydrogen concentration and pressure may be substantially the same,

the maximum catalyst bed temperature will be in the range of about 600 F. to about 860 F. while the liquid hourly space velocity is in the range of about 0.5 to about 4.0. In order to assure that the catalyst bed temperature does not exceed the maximum allowed, conventional quench streams, either normally liquid or normally gaseous and introduced at one or more intermediate loci of the catalyst bed, may be utilized. Before describing my invention, -with reference to the accompanying drawing, several definitions are believed necessary in order that a clear understanding be obtained. In the present speciiication and appended claims, a pressure substantially the same as or temperature substantially the same as, is intended to connote the pressure or temperature under which a downstream vessel is maintained allowing for the normal pressure drop due to fluid iow, and the normal temperature loss due to transfer of material from one zone to another. Thus, where the first hydrocracking reaction zone is at a pressure of about 2,650 p.s.i.g., and the temperature of the eiuent may be as high as 875 F., the first separation zone will function at a pressure of about 2,550 p.s.i.g. and a temperature of about 50 F. lower. Similarly, the second separation zone, or hot flash chamber, will function at a signicantly reduced pressure in the range of about 100 p.s.i.g. to about 300 p.s.i.g. and a temperature perhaps 100 F. lower.

In further describing the process encompassed by my invention concept, reference will be made to the accompanying drawing, which illustrates one embodiment of the invention. For the purpose of demonstrating the ernbodiment illustrated, the drawing will be described in connection with a commercially-scaled unit having a fresh feed charge rate of about 4,500 barrels per day. It is understood that the charge stock, compositions, operating conditions, vessel designs, separators, catalysts and the like, are exemplary only, and may be varied widely without departure from my invention, the scope and spirit of which is dened by the appended claims.

DESCRIPTION OF DRAWING In the drawing, the embodiment is illustrated by means of a simpliiied ow diagram in which such details as pumps, instrumentation and controls, heat-exchange and heat-recovery circuits, start-up lines, compressors, valving and similar hardware have been omitted as being nonessential to an understanding of the techniques involved. The utilization of such miscellaneous appurtenances, to modify the process, are Well within the purview of one skilled in the art of petroleum rening techniques.

The fresh feed charge stocks, being a waxy distillate and deresined oil, are derived from a full boiling range crude stock. The waxy distillate constitutes about 28.3 vol. percent of the crude, while the Cylinder stock constitutes 16.6 vol. percent of which about 16.0% is the deresined oil. The charged stocks have the characteristics indicated in the following Table l:

TABLE 1.-CHARGE STOCK PROPERTIES *Dewaxed V.I. of about 98.

With reference now to the drawing, the deresined oil in line l is admixed with a recycled, hydrogen-rich vaporous phase in line 2, the latter containing make-up hydrogen introduced by way of line 3. The hydrogen concentration is about 10,000 sci/bbl., and total hydrogen consumption is 1121 sci/bbl., or about 1.92% by weight, based upon the total fresh feed, inclusive of both the deresined oil and the waxy distillate. Prior to entering heater 4, the hydrogen/deresiner oil mixture is subjected to heat-exchange with various hot eiiiuent streams (not illustrated), the heater serving to increase the temperature to a level such that the maximum catalyst bed temperature is controlled at about 825 F. The heated mixture passes through line 5 into hydrocracking reactor 6 under an imposed pressure of about 2,500 p.s.i.g. and at an LHSV (liquid hourly space velocity) of 0.5. Reactor 6 has disposed therein a catalyst containing 1.8% by weight of nickel and 16.0% by weight of molybdenum composited with an amorphous carrier material of 63.0% by weight of alumina and 37.0% by weight of silica. The product eiuent is withdrawn by way of line 7 and passes into hot separator 8 at substantially the same pressure and temperature. Hot separator 8 serves to provide a principally liquid phase, containing some hydrocarbons boiling about 825 F., which is introduced by Way of line 9 into hot iiash zone 10 at a reduced pressure of about to about 300 p.s.i.g. A principally vaporous phase is Withdrawn from hot separator 8 through line 12, and is introduced thereby into a second hydrocracking reactor 13.

The waxy distillate portion of the fresh feed enters the process by way of line 14 and, following heatexchange is introduced into heater 15. The heated charge passes through line 16 and is admixed with the hot vaporous phase in line 12. As a result of this technique, the duty imposed upon heater 15 is signilicantly decreased. Furthermore, since the vaporous phase from hot separator 8 is suiiiciently rich in hydrogen, only one compressor system is required to maintain a hydrogen atmosphere in both hydrocracking reactors 6 and 13. Allowing for the normal pressure drop in the system, reactor 13 will function at a level of about 2,350 p.s.i.g. Heater 15 is controlled by monitoring the maximum catalyst bed temperature at a level of about 715 F. The catalyst is identical to that disposed in reactor 6 and the LHSV therethrough is 1.0. Product eiuent, at a temperature of about 715 F., passes from reactor 13 through line 17 into hot separator 18 at substantially the same temperature and pressure. A principally vaporous phase is removed through line 19, and is introduced thereby into cold separator 20. Prior to entering cold separator 20, the hot vaporous phase is utilized as a heat-exchange medium, and then condensed in order to lower its temperature to a level in the range of about 60 F. to about 140 F. A hydrogen-rich vaporous phase is Withdrawn by way of line 2, and recycled therethrough to combine with the deresined oil in line 1. This stream may be treated by any suitable, well known technique for the removal of hydrogen sulfide and light, normally gaseous hydrocarbons in order to increase the hydrogen purity.

A pincipally liquid phase is removed from cold separato 20 in Iline 21, and passes therethrough into cold dash zone 22. The temperature is substantially unchanged, but the pressure is reduced to a level in the range of from 0 p.s.i.g. to about 150 p.s.i.g. Also being introduced into cold ash zone 22 is a vaporous phase in line 11 from hot ash zone 10. The principally liquid phase from hot separator 18 passes through line 23 into a second hot flash zone 24, the vaporous phase from which is also introduced by way of line 25 into cold ilash zone 22. Although not illustrated in the drawing, the vaporous phases in lines 11 and 25 are utilized as heat-exchange media, and further cooled to a temperature of 60 F. to F. Light hydrocarbons and some hydrogen and hydrogen sulfide are vented from the process through line 38. Normally liquid hydrocarbons from hot flash zone 24,

in line 26 and from cold ash zone 22, in line 32, are combined and pass into fractionator 33.

The principally liquid phase from hot flash zone 10, containing those heavier hydrocarbons boiling above a temperature of about 900 F., is removed through line 27 and passes therethrough into vacuum column 28. The vacuum column functions at substantially the same temperature as the liquid phase in line 27, but at a reduced pressure below about 100 mm. Hg, absolute. A waxy bright stock is withdrawn by way of line 31, and excess over that required to produce the desired amount of bright stock may be recycled therethrough to combine with the heated deresined oil in line 5, or with the fresh deresined oil in line 1. Any material boiling below a temperature of about 600 F. to about 650 F. is removed from vacuum column 28 through line 29, and is introduced into fractionator 33 via line 32 in admixture with the principally liquid phase from cold flash zone 22. In one particular embodiment, this relatively lighter material may be employed as a diluent for the heavier bright stock, and recycled therewith to hydrocracking reactor 6. Waxy lubricating oil base stock, suitable for neutral oil production may be removed from vacuum column 28 via line 30 or may be left in stream 31 to produce a wide boiling range, lower viscosity bright stock.

Fractionator 33 is maintained under conditions of pressure and temperature which result in the desired waxy lube oil base stock being removed as a bottoms stream in line 37 which, when combined with the lube oil stream in line 30, constitutes the product of the process. In additional to the lube oil fraction in line 37, one typical product separation effected in fractionator 33 results in a naphtha boiling range fraction in line 34 (i.e. 400 F. -minus), a kerosene cut in line 35 (400 F. to 525 F.) and a diesel oil fraction in line 36 (i.e. 525 F. to 600 F.).

With respect to the waxy lubricating oil base stock being recovered by way of line 37, inclusive of that which is withdrawn from vacuum column 28 by way of line 30, the volume percent recovery is about 70.0, based upon total fresh feed, the viscosity index is 118.8, the 100 F./SUS viscosity is 81.11 and the 210 F./SUS is 38.08. Following the dewaxing procedure of the prior art, which removes about 13.0 vol. percent wax, based upon fresh feed, the viscosity index is about 110, the 100 F./SUS is 82.87 and the 210 F./SUS viscosity is about 38.08.

The bright stock in line 31 is recovered in an amount of 68.0 vol. percent, based upon total fresh feed, and the viscosity index is about 133. Upon dewaxing, the bright stock indicates a viscosity index of about 123.5, and an additional 15.0 vol. percent of wax is removed.

The foregoing specification, and especially the illutrative example integrated into the description of the accompany drawing, clearly indicates the method of effecting the present invention and the benefits afforded through the utlization thereof in the production of lubricating oil base stocks.

I claim as my invention:

1. A process for producing a lubricating oil base stock which comprises the steps of:

(a) reacting a first hydrocarbon charge stock and hydrogen in a first hydrocracking reaction zone, at hydrocracking conditions, in contact with a hydrocracking catalyst;

(b) separating the resulting first zone effluent, at substantially the same temperature and pressure in a first separation zone, to provide a first principally vaporous phase and a first principally liquid phase;

(c) reacting said rst vapor phase and a second, lower-boiling hydrocarbon charge stock in a second hydrocracking reaction zone, at lower severity hydrocracking conditions, and in contact with a hydroracking catalyst;

(d) separating the resulting second zone effluent at substantially the same pressure and temperature, in

a second separation zone, to provide a second principally vaporous phase and a second principally liquid phase;

(e) separating said second vaporous phase, at substantially the same press-ure and at a lower temperature in the range of about 60 F. to about 140 F., in a third separation zone, to provide a hydrogenrich third vaporous phase and a third principally liquid phase;

(f) recycling at least a portion of said hydrogen-rich third vaporous phase to combine with said first hydrocarbon charge stock; and,

(g) separating said first, second and third liquid phases to recover said lubricating oil base stock.

2. The process of claim 1 further characterized in that said first hydrocarbon charge stock has an initial boiling point in the range of about 800 F. to about 925 F.

3. The process of claim 1 further characterized in that said second hydrocarbon charge stock has an initial boiling point above about 600 F.

4. The process of claim 1 further characterized in that the hydrocracking conditions, imposed upon said first hydrocracking reaction zone include a maximum catalyst bed temperature of from about 700 F. to about 900 F. and a liquid hourly space velocity of from 0.3 to about 3.0.

5. The process of claim 1 further characterized in that said lower severity hydrocracking conditions include a higher liquid hourly space velocity in the range of 0.5 to about 4.0, a lower maximum catalyst temperature of from 600 F. to about 860 F., or both a higher liquid hourly space velocity and a lower maximum catalyst bed temperature.

6. The process of claim 1 further characterized in that said first, second and third liquid phases are separated to recover said lubricating oil base stock by the steps of:

(a) separating said first liquid phase in a fourth separation zone, at substantially the same temperature and at a reduced -pressure to provide a fourth vaporous phase and a fourth liquid phase;

(b) separating said second liquid phase in a fifth separation zone, at substantially the same temperature and at a reduced pressure, to provide a fifth vaporous phase and a fifth liquid phase;

(c) separating said third liquid phase, said fourth vaporous phase and said -fifth vaporous phase in a sixth separation zone, at a temperature in the range of 60 F. to about 140 F. and a further reduced pressure, to provide a sixth liquid phase and a sixth vaporous phase;

(d) further separating said fourth liquid phase at substantially the same temperature and at sulbatmospheric pressure, in a seventh separation zone, to provide a seventh liquid phase, an eighth liquid phase and a ninth lubricating oil base stock liquid phase;

(e) further separating said fifth, sixth and eighth liquid phases in an eighth separation zone to provide a tenth lubricating oil base stock liquid phase; and,

(f) combining said ninth and tenth liquid phases to recover said lubracating oil base stock.

7. The process of claim 6 further characterized in that said fourth and fifth separation zones are maintained under a pressure of from p.s.i.g. to about 300 p.s.i.g.

8. The process of claim 6 further characterized in that said sixth separation zone is maintained under a pressure of from atmospheric to about p.s.i.g.

9. The process of claim 6 further characterized in that said eighth separation zone is maintained at conditions of temperature and pressure selected to maintain the initial boiling point of said tenth fraction in the range of about 600 F. to about 700 F.

10. The process of claim 1 further characterized in that said hydrocracking catalysts contain at least one metallic 11 l2 component from Groups VI-B and VII combined with a 3,544,448 12/ 1970 Jacobs et al. 208-59 porous carrier material. 3,551,323 12/1970 Hamblin 208-59 References Cited HERBERT LEVINE, Primary Examiner 5 UNITED S'IATES. PATENTS Us. CL XR. 3,159,565 12/1964 Klmberhn et al 208-78 3,321,395 5/1967 Paterson 2018-78 203`1378=100 102 104 

100. THE HEAVIER PORTION OF THE CARGE STOCK, HAVING AN INITIAL BOILING POINT IN THE RANGE OF ABOUT 800*F.TO ABOUT 925*F., IS SEPARATELY PROCESS IN A FIRST STAGE. THE FROT END OF THE RESULTING PRODUCT EFFUENT IS PROCESED IN A SECOND STAGE, IN ADMIXTURE WITH THE LIGHTER PORTION OF THE CHARGE STOCK HAVING AN END BOILING POINT IN THE RANGE OF ABOUT 800*F. TO ABOUT 925*F. A SERIES OF SEPARATION STEPS IS EMPLOYED TO RECOVER THE LUBRICATING OIL BASE STOCK WHILE CONCENTRATING A HIGH VISCOSITY INDEX BRIGHT STOCK 